1. Field of the Invention
The present invention relates to an inkjet recording apparatus and an ink jet recording system that can carry out multi-pass recording, in which an image is recorded on a unit area of a recording medium during a plurality of operations of a recording head.
2. Description of the Related Art
Conventionally, multi-pass recording is widely known as a technique for recording an image on a single recording area of a recording medium during a plurality of operations of a recording head. Conventionally, such multi-pass recording reduces deterioration in image quality caused by variation in the amount of ink discharged by each recording nozzle of the recording head. The multi-pass recording utilizes a mask pattern as a division pattern for dividing image data corresponding to a single recording area into image data corresponding to a plurality of operations of the recording head. As examples of such mask pattern, the following mask patterns are known.
For example, FIGS. 6B and 6C of Japanese Patent Application Laid-Open No. 2005-297212 illustrate mask patterns in which recordable pixels are narrowly and widely distributed, respectively. Hereinafter, a mask pattern in which recordable pixels are widely distributed is referred to as a distribution mask, and a mask pattern in which recordable pixels are narrowly distributed is referred to as a concentration mask.
Meanwhile, the granularity of ink dots is a factor that determines the quality of an image recorded by the ink jet recording. Since the surface of a recording medium is covered with dots in high duty areas of an image, the granularity of dots is rarely problematic. However, since dots are easily noticeable on the surface of a recording medium in low duty areas of an image, the granularity is easily increased. Thus, conventionally, the multi-pass recording utilizes a distribution mask to reduce the granularity.
In recent years, with increased demand for further improvement in light or water resistance of a recording medium, ink using pigment as a color material has been developed. However, regarding such pigment ink, since color material does not easily penetrate into the inner part of a recording medium, the evenness of the surface is decreased, and the glossiness of the image is thus decreased. Particularly, this decrease in the glossiness can be significant in the multi-pass recording, and the reasons will be described below with reference to FIGS. 7A to 7F.
FIGS. 7E to 7F illustrate adjacent ink dots recorded by a single scanning and recording operation (also referred to as a recording pass). An ink dot discharged from a recording head is composed of pigment, solvent, and moisture. After applied to the surface of a recording medium, while the moisture and the solvent are absorbed by the recording medium, the pigment remains on the surface of the recording medium, as illustrated in FIG. 7F. When adjacent ink dots are recorded at the same recording pass, the ink dots are applied with almost no time lag. Thus, the dots come into contact with each other on the recording medium, and the pigment remains on the surface of the recording medium. Since the unevenness of the surface is small in this case, a decrease in the glossiness of the image is small.
In contrast, FIGS. 7A to 7D illustrate adjacent ink dots each recorded at a different recording pass. When adjacent ink dots are recorded at different recording passes, since the ink dots are applied with a time lag, the dots applied first and next overlap each other.
In this case, as illustrated in FIG. 7D, the pigment remains on the surface unevenly, and the glossiness of the image is decreased. Particularly, when a larger amount of ink is used, more dots overlap one another. Thus, the evenness of the surface is further decreased, and the glossiness is accordingly decreased further. Namely, the glossiness is more likely to be decreased in high duty areas than in low duty areas.
To solve the problem of a decrease in the glossiness in the multi-pass recording, a method using a concentration mask has been known (Japanese Patent Application Laid-Open No. 2005-297212). The method will be described with reference to FIGS. 8A to 8D and FIGS. 9A and 9B.
FIGS. 8A to 8D schematically illustrate surfaces of a high duty area of a recording medium on which an image is recorded by four recording passes. FIGS. 8A to 8C schematically illustrate dots discharged by using a distribution mask of FIG. 9A, and FIG. 8D schematically illustrates dots discharged by using a concentration mask of FIG. 9B. When the distribution mask of FIG. 9A is used, as illustrated in FIG. 8C, ink dots discharged at different passes and are then overlapped with each other, exhibiting a large unevenness. In contrast, when the concentration mask of FIG. 9B is used, as illustrated in FIG. 8D, since dots are discharged at a single pass and are then located adjacent to one another, the unevenness of the surface is small.
As described with reference to FIGS. 7A to 7F, if the surface evenness is higher, the recording medium maintains a higher glossiness. Thus, while use of a distribution mask decreases the glossiness, use of a concentration mask allows the recording medium to maintain a high glossiness.
Based on this knowledge, the method discussed in Japanese Patent Application Laid-Open No. 2005-297212 utilizes the concentration mask when recording an image on a recording medium with a high glossiness and utilizes the distribution mask when recording an image on a recording medium with a low glossiness. However, in the case of a recording medium having glossiness such as glossy paper, the method discussed in Japanese Patent Application Laid-Open No. 2005-297212 cannot solve both of the problems relating to the glossiness and the granularity together.
As described above, a different duty poses a different problem in the ink jet recording. Namely, since both low duty areas and high duty areas are processed with an identical mask according to the above method, the glossiness cannot be improved while maintaining the granularity of an image at a low level.